Thirty years activities in Semnan industrial complex (SIC) have arisen concerns on accumulation of heavy metals in surface soil. The objectives of this study were to determine the concentration and spatial distribution of Pb, Zn, Cu, Ni, Cd and Cr in surface soils of SIC and surrounding areas and to identify origin of these heavy metals. Study area was divided into seven geomorphic units according to landforms and parent materials diversity. Ninety-three composite surface (0-10 cm) soil samples were collected in an area of 117 km2. Concentrations of heavy metals were measured in aqua-regia extracts, using atomic absorption spectrometry. Average concentrationsof Pb, Zn, Cd, Cu, Ni and Cr were 49.2,84.4, 1.6, 22, 20.1 and 9.7 mg kg-1with ranges of 11.6-511.2, 34.1-247.9, 0.7-2.8, 16.9-42.0, 9.2-27.9 and 3.5-22.3 mg kg-1, respectively. The maximum concentrations of Pb, Zn, Cd and Cu were found in the SIC. The spatial distribution of these heavy metals indicated gradual increase in concentrations along the prevailing wind direction. Concentrations of Ni and Cr did not show any specific spatial distribution pattern in relation to activities in SIC and other geomorphic units. According to the principal components analysis results, PC1 with the highest loadings for Pb, Zn, Cd and Cu was recognized as anthropogenic components, whereas the PC2 including Ni and Cr was lithogenic components. The cluster analysis also showed similar grouping. The results indicated considerable increasing in the Pb, Zn and Cd concentrations in the soil, during nearly short period of industrialization. It should be consider to make necessary decision to prevent more pollution.

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